Method for fabricating a semiconductor integrated chip

ABSTRACT

The present invention relates to a compound semiconductor integrated circuit chip having a front and/or back surface metal layer used for electrical connection to an external circuit. The compound semiconductor integrated circuit chip (first chip) comprises a substrate, an electronic device layer, and a dielectric layer. A first metal layer is formed on the front side of the dielectric layer, and a third metal layer is formed on the back side of the substrate. The first and third metal layer are made essentially of Cu and used for the connection to other electronic circuits. A second chip may be mounted on the first chip with electrical connection made with the first or the third metal layer that extends over the electronic device in the first chip in the three-dimensional manner to make the electrical connection between the two chips having connection nodes away from each other.

CROSS-REFERENCE TO RELATED DOCUMENTS

The present invention is a continuation-in-part (CIP) application ofU.S. patent application Ser. No. 14/674,849 entitled “SemiconductorIntegrated Circuit” filed on Mar. 31, 2015. Application Ser. No.14/674,849 was a CIP application of U.S. patent application Ser. No.13/751,855 entitled “Semiconductor Integrated Circuit” filed on Jan. 28,2013.

FIELD OF THE INVENTION

The present invention relates to a semiconductor integrated circuit chiphaving a front and/or back surface metal layer used for electricalconnection to an external circuit, and more particularly to asemiconductor integrated circuit with multiple stacked electroniccircuit chips, in which at least one of them is a compound semiconductorMIMIC chip.

BACKGROUND OF THE INVENTION

Compound semiconductor monolithic microwave integrated circuits (MMICs)have been widely used for the RF transmitter, receiver, and transceiverin microwave communication devices such as cell phones and wireless LANmodules. The RF modules are composed of many circuit elements such aspower amplifiers (PAs), switches, filters, and control devices. Some ofthose circuit elements are integrated in one chip. A compoundsemiconductor amplifier (HBT or HEMT) often uses circuits using HEMTsfor controlling the transistor bias condition. Those circuits can beintegrated in one compound semiconductor chip. For example, theintegration of HBTs and HEMTs is achieved by using a BiFET (or BiHEMT)process, in which both HBT PAs and HEMT control circuits are fabricatedin a compound semiconductor chip. Another example is to use a process inwhich enhancement-mode HEMTs and depletion-mode HEMTs are integrated.The enhancement-mode HEMTs are used for a PAs and the depletion-modeHEMTs are used for the control circuits. A compound semiconductoramplifier (HBT or HEMT) and a switch circuit that changes the RF signalpath depending on the output power level, frequency band, and thecommunication mode are also often integrated in one chip. A compoundsemiconductor amplifier (HBT or HEMT) and an antenna switch circuit thatswitches the connection of the antenna to different Tx and Rx circuitsare also often integrated in one chip. The compound semiconductor HBT PAis often operated at different bias conditions for the different outputpowers and frequencies to maintain an optimal performance. Since theinput and output impedances are functions of the bias condition, animpedance tuner is introduced to maintain a good impedance matching inaccordance with the change in the bias condition. The impedance tunerusually consists of capacitors, inductors and HEMT switches. The HEMTswitch is used to change the connection of the capacitor and inductor tochange the overall impedance. The high integration of circuit elementsinduces high process cost and low process yield. That is particularlythe case when both HBT and HEMT are integrated on one chip.

To reduce the process cost, the circuit elements of the RF moduledescribed above can be formed on separate chips, and other electronicchips such as Si CMOS chip can be included. Conventionally, the chipsare placed in one plane. However, the use of multiple chips in one planemakes the module size large, and the long interconnection between thosechips induces signal loss and interference. An example of such an RFmodule is the one consisting of an HBT PA MIMIC chip, impedance matchingand bias control chip, an antenna switch chip, and a filter circuitchip, all of which are placed in one plane on the module substrate.

SUMMARY OF THE INVENTION

The present invention provides a compound semiconductor integratedcircuit chip having a front and/or back surface metal layer used forelectrical connection to an external circuit. Its main object is toprovide a semiconductor integrated circuit, which comprises stackedelectronic chips, in which at least one of the chips is a compoundsemiconductor electronic integrated circuit chip. The footprint of amodule composed of the semiconductor integrated circuit with stackedchips can be reduced significantly. The manufacturing processes of thechips are reduced compared with the case in which the circuit elementsare integrated in one chip. The interconnections between chips orbetween two circuit elements can be made short, and thereby the signalloss and interference can be reduced. The metal layer formed over thedevice active region make it possible to connect nodes in two chips atpositions apart from each other horizontally, and thereby there is morefreedom in the layout design of the connection nodes.

To reach the objects stated above, the present invention provides asemiconductor integrated circuit comprising a first chip, which containsa compound semiconductor integrated circuit. The first chip comprises asubstrate, a dielectric layer, an electronic device layer, and a firstmetal layer. The dielectric layer is formed above the substrate and hasat least one dielectric layer via hole penetrating from a first surfaceto a second surface of the dielectric layer. The first metal layer ismade essentially of Cu. The first metal layer forms at least one firstpad on the first surface of the dielectric layer and extends into onedielectric layer via hole. The electronic device layer is formed betweenthe substrate and the dielectric layer and contains at least oneelectronic device including at least one compound semiconductorelectronic device and at least one second metal layer, in which at leastone of the at least one second metal layer is connected to the at leastone electronic device, and at least one of the at least one second metallayer also forms at least one second pad placed at the end of onedielectric layer via hole at the second surface of the dielectric layer,at which the second pad is electrically connected to the first metallayer that extends into the dielectric layer via hole. All of the atleast one second metal layer in contact with the at least one compoundsemiconductor electronic device is made essentially of Au. At least onefirst pad is electrically connected to the second pad at the other endof the dielectric layer via hole by the first metal layer that extendsover at least one of the at least one electronic device in theelectronic device layer.

Furthermore, the present invention provides a semiconductor integratedcircuit, which comprises the aforementioned first chip and a secondchip. The second chip contains an electronic circuit. The first surfaceof the dielectric layer of the first chip defines the front surface ofthe first chip, and the surface of the substrate of the first chipopposite to the dielectric layer defines the back surface of the firstchip. The second chip is stacked on the front surface of the first chipand electrically connected to the at least one first pad. To align theelectrical connection points in the two chips, the at least one firstpad is electrically connected to the second pad at the other end of thedielectric layer via hole by the first metal layer that extends over atleast one of the at least one electronic device in the electronic devicelayer.

The present invention also provides a method for fabricating asemiconductor integrated circuit described above, comprising the processsteps below in the same order:

-   -   1. growing at least one compound semiconductor epitaxial layer        on a substrate of a chip;    -   2. fabricating at least one compound semiconductor electronic        device on the substrate using the at least one compound        semiconductor epitaxial layer;    -   3. depositing at least one second metal layer made essentially        of Au above the at least one compound semiconductor epitaxial        layer to form an electrical connection to at least one of the at        least one compound semiconductor electronic device, and also to        form at least one second pad;    -   4. depositing a SiN layer above the at least one second metal        layer for passivation or protection of the at least one compound        semiconductor electronic device (hereafter, the layer comprising        the at least one compound semiconductor electronic device, the        at least one second metal layer, and the SiN layer as an        electronic device layer);    -   5. depositing a dielectric layer above the electronic device        layer;    -   6. forming at least one dielectric layer via hole penetrating        through the dielectric layer for the electrical contact to the        at least one second pad; and    -   7. depositing a first metal layer made essentially of Cu on the        dielectric layer forming at least one first pad on the        dielectric layer, extending from the each first pad into the at        least one dielectric layer via hole and connecting to the at        least one second pad, where the first metal layer extends from        at least one of the at least one first pad three-dimensionally        over at least one of the at least one compound semiconductor        device, then into the at least one dielectric layer via hole and        connects to the at least one second pad.

In the fabrication method described above, the electronic device layeris formed on the substrate as a front-end process. The topmost surfaceis protected by SiN. The process containing Cu, on the other hand, isperformed on the surface protected by SiN. In this way, thecontamination of compound semiconductor device by Cu is prevented. Thefirst pad may be used to connect another chip to the chip.

The present invention provides another semiconductor integrated circuitcomprising a first chip and a second chip, in which the first chipcontains a compound semiconductor integrated circuit and the second chipcontains an electronic circuit. The first chip comprises a substrate, adielectric layer, an electronic device layer, a first metal layer, and athird metal layer. The substrate has at least one through substrate viahole penetrating from a front side to a backside of the substrate. Thedielectric layer is formed above the front side of the substrate and hasat least one dielectric layer via hole penetrating from a first surfaceto a second surface of the dielectric layer. The first metal layer ismade essentially of Cu. The first metal layer forms at least one firstpad on the first surface of the dielectric layer and extends into onedielectric layer via hole. The electronic device layer is formed betweenthe substrate and the dielectric layer and contains at least oneelectronic device including at least one compound semiconductorelectronic device and at least one second metal layer, in which at leastone of the at least one second metal layer is connected to the at leastone electronic device, at least one of the at least one second metallayer also forms at least one second pad placed at the end of onedielectric layer via hole at the second surface of the dielectric layer,at which the second pad is electrically connected to the first metallayer that extends into the dielectric layer via hole, and at least oneof the at least one second metal layer also forms at least one third padat the end of the through substrate via hole at the front side of thesubstrate. All of the at least one second metal in contact with the atleast one compound semiconductor electronic device is made essentiallyof Au. The third metal layer forms at least one fourth pad on thebackside of the substrate and extends into one through substrate viahole to make an electrical connection to the third pad disposed at theother end of the through substrate via hole. The first surface of thedielectric layer defines the front surface of the first chip, and thebackside of the substrate defines the back surface of the first chip.The second chip is stacked on the back surface of the first chip andelectrically connected to the at least one fourth pad. To align theelectrical connection points in the two chips, the first pad iselectrically connected to the second pad at the other end of thedielectric layer via hole by the first metal layer that extends over atleast one of the at least one electronic device in the electronic devicelayer.

The present invention also provides a method for fabricatingsemiconductor integrated circuit described above, comprising the processsteps below in the same order:

-   -   1. growing at least one compound semiconductor epitaxial layer        on a substrate of a chip;    -   2. fabricating at least one compound semiconductor electronic        device on the substrate using the at least one compound        semiconductor epitaxial layer;    -   3. depositing at least one second metal layer made essentially        of Au above the at least one compound semiconductor epitaxial        layer to form an electrical connection to at least one of the at        least one compound semiconductor electronic device, and also to        form at least one second pad and at least one third pad;    -   4. depositing a SiN layer above the at least one second metal        layer for passivation or protection of the at least one compound        semiconductor electronic device (hereafter, the layer comprising        the at least one compound semiconductor electronic device, the        at least one second metal layer, and the SiN layer as an        electronic device layer);    -   5. depositing a dielectric layer above the electronic device        layer;    -   6. forming of at least one dielectric layer via hole penetrating        through the dielectric layer for the electrical contact to the        at least one second pad;    -   7. depositing a first metal layer made essentially of Cu on the        dielectric layer forming at least one first pad on the        dielectric layer, extending from the each first pad into the at        least one dielectric layer via hole and connecting to the at        least one second pad, where the first metal layer extends from        at least one of the at least one first pad three-dimensionally        over at least one of the at least one compound semiconductor        device, then into the at least one dielectric layer via hole and        connects to the at least one second pad;    -   8. forming of at least one through substrate via hole        penetrating through the substrate from a backside of the        substrate reaching the at least one third pad; and    -   9. depositing third metal layer on the backside of the substrate        forming at least one fourth pad on the backside of the        substrate, extending from the each fourth pad into the at least        one through substrate via hole and connecting to the at least        one third pad.

In the fabrication method described above, the electronic device layeris formed on the substrate as a front-end process. The topmost surfaceis protected by SiN. The process containing Cu, on the other hand, isperformed on the surface protected by SiN. In this way, thecontamination of compound semiconductor device by Cu is prevented. Thefourth pad may be used to connect another chip to the chip.

The present invention provides another semiconductor integrated circuitcomprising a first chip and a second chip, in which the first chipcontains a compound semiconductor integrated circuit and the second chipcontains an electronic circuit. The first chip comprises a substrate, anelectronic device layer, and a third metal layer. The substrate has atleast one through substrate via hole penetrating from a front side to abackside of the substrate. The electronic device layer is formed on thefront side of the substrate and contains at least one electronic deviceincluding at least one compound semiconductor electronic device and atleast one second metal layer, in which at least one of the at least onesecond metal layer is connected to the at least one electronic device,and at least one of the at least one second metal layer also forms atleast one third pad at the end of the through substrate via hole at thefront side of the substrate. The third metal layer forms at least onefourth pad on the backside of the substrate and extends into one throughsubstrate via hole to make an electrical connection to the third paddisposed at the other end of the through substrate via hole. The thirdpad is electrically connected, directly or indirectly, by the at leastone second metal layer to at least one of the at least one electronicdevice. The third pad may also be connected to a fifth pad formed by theat least one second metal layer and placed at or in the vicinity of thesurface of the electronic device layer opposite to the substrate. Thefifth pad may further connected to other circuit chips or electronicmodules. The surface of the electronic device layer opposite to thesubstrate defines the front surface of the first chip, and the backsideof the substrate defines the back surface of the first chip. The secondchip is stacked on the back surface of the first chip and electricallyconnects to the fourth pad. To align the electrical connection points inthe two chips, the fourth pad is electrically connected to the third padat the other end of the through substrate via hole by the third metallayer that extends over one of the at least one electronic device in theelectronic device layer.

The present invention also provides a method for fabricatingsemiconductor integrated circuit described above, comprising the processsteps below in the same order:

-   -   1. growing at least one compound semiconductor epitaxial layer        on a substrate of a chip;    -   2. fabricating at least one compound semiconductor electronic        device on the substrate using the at least one compound        semiconductor epitaxial layer;    -   3. depositing at least one second metal layer made essentially        of Au above the at least one compound semiconductor epitaxial        layer to form an electrical connection to at least one of the at        least one compound semiconductor electronic device, and also to        form at least one third pad;    -   4. forming at least one through substrate via holes penetrating        through the substrate from a backside of the substrate reaching        the at least one third pad; and    -   5. depositing third metal layer made essentially of Cu on the        backside of the substrate forming at least one fourth pad on the        backside of the substrate, extending from the each fourth pad        into the at least one through substrate via hole and connecting        to the at least one third pad, where the third metal layer        extends from at least one of the at least one fourth pad        three-dimensionally over at least one of the at least one        compound semiconductor device, then into the at least one        through substrate via hole and connects to the at least one        third pad.

In the fabrication method above, the electronic device layer is formedas a front-end process made on the substrate. The process containing Cu,on the other hand, is made on the backside of the substrate. In thisway, the contamination of compound semiconductor device by Cu isprevented. The fourth pad may be used to connect another chip to thechip. The use of Cu for the third metal layer reduces the signal lossdue to the electrical connection between the main compound semiconductorintegrated circuit and another chip.

Another object of the present invention is to provide a semiconductorintegrated circuit, in which the back side metal layer of a chip canform an inductor. The inductor on the back side of the chip further savethe space the whole circuit occupies, and therefore the chip size can bereduced. The high quality factor for the inductor on the back side ofthe chip can be obtained when the back side metal layer contains Cu.

To reach the object stated above, the present invention provides anothersemiconductor integrated circuit, which further includes an inductor inthe semiconductor integrated circuit described above. The inductor isformed by the third metal layer on the backside of the substrate of thefirst chip over at least one of the at least one electronic device. Theinductor is electrically connected to the first chip, the second chip,or both the first chip and the second chips.

In implementation, all of the at least one second metal layer are madeessentially of Au.

In implementation, the substrate of the first chip described above ismade of GaAs.

In implementation, the dielectric layer described above is made ofPolybenzoxazole (PBO).

In implementation, the thickness of the dielectric layer described aboveis 10 μm or thicker.

In implementation, the third metal layer is made essentially of Cu.

In implementation, the first chip described above contains aheterojunction bipolar transistor (HBT) monolithic microwave integratedcircuit (MMIC) or a high electron mobility transistor (HEMT) MMIC.

In implementation, the first chip described above contains a GaN fieldeffect transistor (FET).

In implementation, the first chip described above contains a poweramplifier MIMIC.

In implementation, the second chip described above contains a biascontrol circuit that controls the bias condition of the at least oneelectronic device in the first chip, a switching circuit that controlsthe signal path in the first chip, an antenna switching circuit thatconnects the output from the power amplifier in the first chip to anantenna, an impedance tuner circuit that gives variable impedancedepending on the bias condition and the operating frequency of the poweramplifier in the first chip, or an impedance matching circuit consistingof passive devices for the impedance matching at the output and/or inputof the power amplifier in the first chip.

In implementation, the second chip described above contains a compoundsemiconductor MIMIC.

In implementation, the second chip described above contains a Sicomplementary metal-oxide-semiconductor (CMOS) integrated circuit.

In implementation, the second chip described above contains at least onepassive device integrated on a substrate made of Si, GaAs, or glass.

In implementation, the second chip described above contains a filter.

The present invention will be understood more fully by reference to thedetailed description of the drawings and the preferred embodimentsbelow.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic showing the cross-sectional view of an embodimentaccording to the present invention, in which the second chip is stackedon the front surface of the first chip.

FIG. 2 is a schematic showing the cross-sectional view of an embodimentaccording to the present invention, in which the second chip is stackedon the back surface of the first chip.

FIG. 3 is a schematic showing the cross-sectional view of anotherembodiment according to the present invention, in which the second chipis stacked on the back surface of the first chip.

FIG. 4 is a schematic showing the cross-sectional view of anotherembodiment according to the present invention, in which an inductor isformed on the back surface of the first chip.

FIG. 5-23 are schematics showing the embodiment 1˜19 provided by thepresent invention.

FIG. 24 is a schematic showing the cross-sectional view of an embodimentof a chip containing a compound semiconductor integrated circuitaccording to the present invention.

FIGS. 24A and 24B are a schematic showing the cross-sectional view ofembodiments of the metal layers according to the present invention.

FIG. 25 is a schematic showing the cross-sectional view of anotherembodiment of a chip containing a compound semiconductor integratedcircuit according to the present invention.

FIG. 26 is a schematic showing the cross-sectional view of anotherembodiment of a chip containing a compound semiconductor integratedcircuit according to the present invention.

DETAILED DESCRIPTIONS OF PREFERRED EMBODIMENTS

FIG. 24 is a schematic showing the cross-sectional view of an embodimentof semiconductor integrated circuit according to the present invention.The semiconductor integrated circuit comprises a first chip 100, whichcontains a compound semiconductor integrated circuit. The first chipcomprises a substrate 110, a dielectric layer 130, an electronic devicelayer 120, and a first metal layer 140. The dielectric layer 130 isformed above the substrate 110 and has at least one dielectric layer viahole 133 penetrating from a first surface of the dielectric layer 131 toa second surface of the dielectric layer 132. The electronic devicelayer 120 is formed between the substrate 110 and the dielectric layer130. The electronic device layer 120 contains at least one compoundsemiconductor electronic device 121 and at least one second metal layer150. The first metal layer 140 forms at least one first pad 141 on thefirst surface of the dielectric layer 131 and extends into onedielectric layer via hole 133. At least one of the at least one secondmetal layer 150 is electrically in contact with the at least onesemiconductor electronic device 121. At least one of the at least onesecond metal layer 150 also forms at least one second pad 151 placed atthe end of one dielectric layer via hole 133 at the second surface ofthe dielectric layer 132, at which the at least one second pad 151 iselectrically connected to the first metal layer 140 that extends intothe dielectric layer via hole 133. As shown in FIGS. 24A and 24B, one ormore bottom layers may be included below the first/second metal layer asan adhesion layer, a diffusion barrier layer, and/or a seed layer forelectroplating. One or more top layers may be included above thefirst/second metal layer for protecting the metal layers from moistureand oxidation, and/or for better adhesion with a material formed on top.The bottom layer for a Cu layer can be made of Ti, TiW, Pd, etc., andthe top layer for a Cu layer can be made of Au, etc. The bottom layerfor a Au layer can be made of Ti, Pd, etc., and the top layer for a Aulayer can be made of Ti, etc. By forming metal bumps 280 on the firstpads 141, the first chip 100 may be connected to other electroniccircuits. Connection to other circuits may also be made by bonding metalwires on the first pads 141 instead of using the metal bumps 280. Forexample, the first chip 100 may be mounted directly on a modulesubstrate with the electrical connection made by bump bonding or wirebonding between the first pad 141 and a pad formed on the modulesubstrate. At least one first pad 141 is electrically connected to thesecond pad 151 at the other end of the dielectric layer via hole 133 bythe first metal layer 140 that extends in a three-dimensional mannerover at least one of the at least one electronic device 121 in theelectronic device layer 120 to place the at least one first pad 141 at alocation favorable for connecting to the other electronic circuits.

The semiconductor integrated circuit shown in FIG. 24 is fabricated bythe process as follows:

First, at least one compound semiconductor epitaxial layers is grown onthe substrate 110. Using the at least one compound semiconductorepitaxial layer, at least one compound semiconductor electronic device(shown as at least one of the at least one electronic device 121 in FIG.24) is fabricated on the substrate 110. At least one second metal layer150 made essentially of Au is deposited above the at least one compoundsemiconductor epitaxial layer to form an electrical connection to atleast one of the at least one compound semiconductor electronic device121, and also to form at least one second pad 151. In FIG. 24, at leastone second metal layer 150 is made of three metal layers stacked oneafter another isolated by dielectric passivation/protection layers 126a-126 d preferably made of SiN. In particular, the topmostpassivation/protection layer 126 d covering the topmost at least onesecond metal layer 150 is SiN. SiN has strong ability as a diffusionbarrier against foreign elements and for moisture protection. Theprocess of fabricating electronic device layer 120 is thus completed byprotecting its surface by SiN. Dielectric layer 130 is then depositedabove electronic device layer 120, and at least one dielectric layer viahole 133 penetrating through dielectric layer 130 for electricalconnection to at least one second pad 151 is formed. If a photosensitivematerial such as polybenzoxazole (PBO) is used for dielectric layer 130,at least one dielectric layer via hole 133 can be photo-patterned in thewhole film formation process. The hole in the topmost SiN layer at thebottom of at least one dielectric layer via hole 133 can be made eitherbefore the deposition of dielectric layer 130 or after the formation ofat least one dielectric layer via hole 133. First metal layer 140 madeessentially of Cu is then deposited on dielectric layer 130 forming atleast one first pad 141 on dielectric layer 130. First metal layer 140extends from the each first pad 141 into at least one dielectric layervia hole 133 and connecting to at least one second pad 151. Here, firstmetal layer 140 is formed in such a way that it extends from at leastone of the at least one first pad 141 three-dimensionally over at leastone of the at least one compound semiconductor device (shown by 121 inFIG. 24), then into at least one dielectric layer via hole 133 andconnects to at least one second pad 151.

In the fabrication method described above, electronic device layer 120is formed as a front-end process made on substrate 110. The topmostsurface is protected by SiN. The process containing Cu, on the otherhand, is made on the surface protected by SiN. In this way, thecontamination of compound semiconductor device by Cu is prevented.

The semiconductor integrated circuit shown in FIG. 25 is fabricated bythe process as follows:

First, at least one compound semiconductor epitaxial layers is grown onsubstrate 110. Using the at least one compound semiconductor epitaxiallayer, at least one compound semiconductor electronic device (shown asat least one of the at least one electronic device 121 in FIG. 25) isfabricated on substrate 110. At least one second metal layer 150 madeessentially of Au is deposited above the at least one compoundsemiconductor epitaxial layer to form an electrical connection to atleast one of the at least one compound semiconductor electronic device121, and also to form at least one second pad 151 and at least one thirdpad 161. In FIG. 25, at least one second metal layer 150 is made ofthree metal layers stacked one after another isolated by dielectricpassivation/protection layers 126 a-126 d preferably made of SiN. Inparticular, the topmost passivation/protection layer 126 d covering thetopmost at least one second metal layer 150 is SiN. SiN has strongability as a diffusion barrier against foreign elements and for moistureprotection. The process of fabricating electronic device layer 120 isthus completed by protecting its surface by SiN. Dielectric layer 130 isthen deposited above electronic device layer 120, and at least onedielectric layer via hole 133 penetrating through dielectric layer 130for electrical connection to at least one second pad 151 is formed. If aphotosensitive material such as polybenzoxazole (PBO) is used fordielectric layer 130, at least one dielectric layer via hole 133 can bephoto-patterned in the whole film formation process. The hole in thetopmost SiN layer at the bottom of at least one dielectric layer viahole 133 can be made either before the deposition of dielectric layer130 or after the formation of at least one dielectric layer via hole133. First metal layer 140 made essentially of Cu is then deposited ondielectric layer 130 forming at least one first pad 141 on dielectriclayer 130. First metal layer 140 extends from the each first pad 141into at least one dielectric layer via hole 133 and connecting to atleast one second pad 151. Here, first metal layer 140 is formed in sucha way that it extends from at least one of the at least one first pad141 three-dimensionally over at least one of the at least one compoundsemiconductor device (shown by 121 in FIG. 25), then into at least onedielectric layer via hole 133 and connects to at least one second pad151.

The process above made on the front surface is then followed by thebackside process. First, substrate 110 is thinned down to a designedthickness by grinding, and at least one through substrate via hole 113is formed to reach at least one third pad 161. Third metal layer 170made preferably of Cu is then deposited on the backside of substrate 110and forms at least one fourth pad 171. Third metal layer 170 alsoextends from at least one fourth pad 171 into at least one throughsubstrate via hole 113, then connects to at least one third pad 161.

In the fabrication method described above, electronic device layer 120is formed as a front-end process made on substrate 110. The topmostsurface is protected by SiN. The process containing Cu, on the otherhand, is made on the surface protected by SiN. In this way, thecontamination of compound semiconductor device by Cu is prevented.

The semiconductor integrated circuit shown in FIG. 26 is fabricated bythe process as follows:

First, at least one compound semiconductor epitaxial layers is grown onsubstrate 110. Using the at least one compound semiconductor epitaxiallayer, at least one compound semiconductor electronic device (shown asat least one of the at least one electronic device 121 in FIG. 26) isfabricated on substrate 110. At least one second metal layer 150 madeessentially of Au is deposited above the at least one compoundsemiconductor epitaxial layer to form an electrical connection to atleast one of the at least one compound semiconductor electronic device121, and also to form at least one third pad 161. In FIG. 26, at leastone second metal layer 150 is made of three metal layers stacked oneafter another isolated by dielectric passivation/protection layerspreferably made of SiN.

The process above made on the front surface is then followed by thebackside process. First, substrate 110 is thinned down to a designedthickness by grinding, and at least one through substrate via hole 113is formed. Third metal layer 170 made essentially of Cu is thendeposited on the backside of substrate 110 and forms at least one fourthpad 171. Third metal layer 170 also extends from at least one fourth pad171 into at least one through substrate via hole 113, then connects toat least one third pad 161. Here, third metal layer 170 is formed insuch a way that it extends from at least one of the at least one fourthpad 171 three-dimensionally over at least one of the at least onecompound semiconductor device (shown by 121 in FIG. 26), then into atleast one through substrate via hole 113 and connects to at least onethird pad 161.

In the fabrication method described above, electronic device layer 120is formed as a front-end process made on substrate 110. The processcontaining Cu, on the other hand, is made on the backside of thesubstrate 110. In this way, the contamination of compound semiconductordevice by Cu is prevented. The use of Cu for third metal layer 170reduces the signal loss due to the electrical connection between themain compound semiconductor integrated circuit and the second chip.

FIG. 1 is a schematic showing the cross-sectional view of an embodimentof a semiconductor integrated circuit according to the presentinvention. The semiconductor integrated circuit comprises theaforementioned first chip 100 and a second chip 200. The second chip 200contains an electronic circuit. The first surface of the dielectriclayer of the first chip 100 defines the front surface 102 of the firstchip, and the surface of the substrate of the first chip 100 opposite tothe dielectric layer defines the back surface 101 of the first chip. Thesecond chip 200 is stacked on the front surface 102 of the first chip100 and electrically connects to the at least one first pad 141 viabumps 280. The stacked first chip and the second chip are thuselectrically connected and integrated into one circuit. To align theelectrical connection between the first chip 100 and the second chip 200by the bumps 280, the first pad 141 is electrically connected to thesecond pad 151 at the other end of the dielectric layer via hole 133 bythe first metal layer 140 that extends in a three-dimensional mannerover the at least one of the at least one electronic device 121 in theelectronic device layer 120.

The semiconductor integrated circuit shown in FIG. 1 is fabricated bythe process as follows:

First, at least one compound semiconductor epitaxial layers is grown onthe substrate 110. Using the at least one compound semiconductorepitaxial layer, at least one compound semiconductor electronic device(shown as at least one of the at least one electronic device 121 inFIG. 1) is fabricated on the substrate 110. At least one second metallayer 150 made essentially of Au is deposited above the at least onecompound semiconductor epitaxial layer to form an electrical connectionto at least one of the at least one compound semiconductor electronicdevice 121, and also to form at least one second pad 151. In FIG. 1, atleast one second metal layer 150 is made of three metal layers stackedone after another isolated by dielectric passivation/protection layers126 a-126 d preferably made of SiN. In particular, the topmostpassivation/protection layer 126 d covering the topmost at least onesecond metal layer 150 is SiN. SiN has strong ability as a diffusionbarrier against foreign elements and for moisture protection. Theprocess of fabricating electronic device layer 120 is thus completed byprotecting its surface by SiN. Dielectric layer 130 is then depositedabove electronic device layer 120, and at least one dielectric layer viahole 133 penetrating through dielectric layer 130 for electricalconnection to at least one second pad 151 is formed. If a photosensitivematerial such as polybenzoxazole (PBO) is used for dielectric layer 130,at least one dielectric layer via hole 133 can be photo-patterned in thewhole film formation process. The hole in the topmost SiN layer at thebottom of at least one dielectric layer via hole 133 can be made eitherbefore the deposition of dielectric layer 130 or after the formation ofat least one dielectric layer via hole 133. First metal layer 140 madeessentially of Cu is then deposited on dielectric layer 130 forming atleast one first pad 141 on dielectric layer 130. First metal layer 140extends from the each first pad 141 into at least one dielectric layervia hole 133 and connecting to at least one second pad 151. Here, firstmetal layer 140 is formed in such a way that it extends from at leastone of the at least one first pad 141 three-dimensionally over at leastone of the at least one compound semiconductor device (shown by 121 inFIG. 1), then into at least one dielectric layer via hole 133 andconnects to at least one second pad 151.

The process steps above describe the essential part of the fabricationof first chip 100. Second chip 200 is then stacked on front surface 102of first chip 100. The electronic circuit in second chip 200 iselectrically connected to at least one of the at least one first pad141. Thus, the electronic circuit in second chip 200 is connected to thesemiconductor integrated circuit in first chip 100. The connection ismade via bumps 280. Bumps 280 are formed beforehand either on chip 100or chip 200.

In the fabrication method described above, electronic device layer 120is formed as a front-end process made on substrate 110. The topmostsurface is protected by SiN. The process containing Cu, on the otherhand, is made on the surface protected by SiN. In this way, thecontamination of compound semiconductor device by Cu is prevented.

FIG. 2 is a schematic showing the cross-sectional view of anotherembodiment of the semiconductor integrated circuit according to thepresent invention. The semiconductor integrated circuit comprises afirst chip 100 and a second chip 200, in which the first chip 100contains a compound semiconductor integrated circuit and the second chip200 contains an electronic circuit. The first chip 100 comprises asubstrate 110, an electronic device layer 120, a dielectric layer 130, afirst metal layer 140, and a third metal layer 170. The substrate 110has at least one through substrate via hole 113 penetrating from a frontside of the substrate 111 to a backside of the substrate 112. Thedielectric layer 130 is formed above the front side of the substrate 111and has at least one dielectric layer via hole 133 penetrating from afirst surface of the dielectric layer 131 to a second surface of thedielectric layer 132. The electronic device layer 120 contains at leastone electronic device including at least one compound semiconductorelectronic device 121 and at least one second metal layer 150, and isformed between the substrate 110 and the dielectric layer 130. The atleast one first metal layer 140 is made essentially of Cu. The firstmetal layer 140 forms at least one first pad 141 on the first surface ofthe dielectric layer 131 and extends into one dielectric layer via hole133. At least one of the at least one second metal layer 150 iselectrically in contact with the at least one compound semiconductorelectronic device 121. All of the at least one second metal layer 150 incontact with the at least one compound semiconductor electronic device121 is made essentially of Au. One of the at least one second metallayer also forms a second pad 151 placed at the end of the dielectriclayer via hole 133 opposite to the first pad 141, at which the secondpad 151 is electrically connected to the first metal layer 140 thatextends into the dielectric layer via hole 133. The third metal layer170 forms at least one fourth pad 171 on the backside of the substrate112 and extends into one through substrate via hole 113. At least one ofthe at least one second metal layer 150 forms at least one third pad 161at the end of one through substrate via holes opposite to the fourth pad171, at which the third pad 161 is electrically connected to the thirdmetal layer 170 that extends into the through substrate via hole 113.One or more bottom layers may be included below the first/second/thirdmetal layer, and/or one or more top layers may be included above thefirst/second/third metal layer, as described previously. The firstsurface of the dielectric layer defines the front surface 102 of thefirst chip 100, and the backside of the substrate defines the backsurface 101 of the first chip 100. In this embodiment, the first chip100 is turned over and the second chip 200 is stacked on the backsurface 101 of the first chip 100 and electrically connects to the atleast one fourth pad 171 via bumps 280. The stacked first chip and thesecond chip are thus electrically connected and integrated into onecircuit. Each of the at least one first pad 141 is further connected toa bump 180 for the electrical connection to other circuit chips orelectronic modules. To align the electrical connection between the firstchip 100 and the second chip 200 by the bumps 280, the first pad 141 iselectrically connected to the second pad 151 at the other end of thedielectric layer via hole 133 by the first metal layer 140 that extendsin a three-dimensional manner over at least one of the at least oneelectronic device 121 in the electronic device layer 120.

The semiconductor integrated circuit shown in FIG. 2 is fabricated bythe process as follows:

First, at least one compound semiconductor epitaxial layers is grown onsubstrate 110. Using the at least one compound semiconductor epitaxiallayer, at least one compound semiconductor electronic device (shown asat least one of the at least one electronic device 121 in FIG. 2) isfabricated on substrate 110. At least one second metal layer 150 madeessentially of Au is deposited above the at least one compoundsemiconductor epitaxial layer to form an electrical connection to atleast one of the at least one compound semiconductor electronic device121, and also to form at least one second pad 151 and at least one thirdpad 161. In FIG. 2, at least one second metal layer 150 is made of threemetal layers stacked one after another isolated by dielectricpassivation/protection layers preferably made of SiN. In particular, thetopmost passivation/protection layer covering the topmost at least onesecond metal layer 150 is SiN. SiN has strong ability as a diffusionbarrier against foreign elements and for moisture protection. Theprocess of fabricating electronic device layer 120 is thus completed byprotecting its surface by SiN. Dielectric layer 130 is then depositedabove electronic device layer 120, and at least one dielectric layer viahole 133 penetrating through dielectric layer 130 for electricalconnection to at least one second pad 151 is formed. If a photosensitivematerial such as polybenzoxazole (PBO) is used for dielectric layer 130,at least one dielectric layer via hole 133 can be photo-patterned in thewhole film formation process. The hole in the topmost SiN layer at thebottom of at least one dielectric layer via hole 133 can be made eitherbefore the deposition of dielectric layer 130 or after the formation ofat least one dielectric layer via hole 133. First metal layer 140 madeessentially of Cu is then deposited on dielectric layer 130 forming atleast one first pad 141 on dielectric layer 130. First metal layer 140extends from the each first pad 141 into at least one dielectric layervia hole 133 and connecting to at least one second pad 151. Here, firstmetal layer 140 is formed in such a way that it extends from at leastone of the at least one first pad 141 three-dimensionally over at leastone of the at least one compound semiconductor device (shown by 121 inFIG. 2), then into at least one dielectric layer via hole 133 andconnects to at least one second pad 151.

The process above made on the front surface is then followed by thebackside process. First, substrate 110 is thinned down to a designedthickness by grinding, and at least one through substrate via hole 113is formed to reach at least one third pad 161. Third metal layer 170 isthen deposited on the backside of substrate 110 and forms at least onefourth pad 171. Third metal layer 170 also extends from at least onefourth pad 171 into at least one through substrate via hole 113, thenconnects to at least one third pad 161.

The process steps above describe the essential part of the fabricationof first chip 100. Second chip 200 is then stacked on back surface 101of first chip 100. The electronic circuit in second chip 200 iselectrically connected to at least one of the at least one fourth pad171. Thus, the electronic circuit in second chip 200 is connected to thesemiconductor integrated circuit in first chip 100. The connection ismade via bumps 280. Bumps 280 are formed beforehand either on chip 100or chip 200.

In the fabrication method described above, electronic device layer 120is formed as a front-end process made on substrate 110. The topmostsurface is protected by SiN. The process containing Cu, on the otherhand, is made on the surface protected by SiN. In this way, thecontamination of compound semiconductor device by Cu is prevented.

FIG. 3 is a schematic showing the cross-sectional view of anotherembodiment of the semiconductor integrated circuit according to thepresent invention. The semiconductor integrated circuit comprises afirst chip 100 and a second chip 200, in which the first chip 100contains a compound semiconductor integrated circuit and the second chip200 contains an electronic circuit. The first chip 100 comprises asubstrate 110, an electronic device layer 120, and a third metal layer170. The substrate 110 has at least one through substrate via hole 113penetrating from a front side of the substrate 111 to a backside of thesubstrate 112. The electronic device layer 120 is formed on the frontside of the substrate 111 and contains at least one electronic device121 and at least one second metal layer 150. The third metal layer 170forms at least one fourth pad 171 on the backside of the substrate 112and extends into the through substrate via hole 113. At least one of theat least one second metal layer 150 forms a third pad 161 at the end ofone through substrate via hole 113 opposite to the fourth pad 171, atwhich the third pad 161 is electrically connected to the third metallayer 170 that extend into the through substrate via hole 113. The thirdpad 161 is electrically connected, directly or indirectly, by the atleast one second metal layer 150 to at least one of the at least oneelectronic device 121 or a fifth pad 181 formed by the at least onesecond metal layer 150 and placed at or in the vicinity of the surfaceof the electronic device layer 120 opposite to the substrate 110. One ormore bottom layers may be included below the second/third metal layer,and/or one or more top layers may be included above the second/thirdmetal layer, as described previously. The surface of the electronicdevice layer opposite to the substrate defines the front surface 102 ofthe first chip, and the backside of the substrate defines the backsurface 101 of the first chip. In this embodiment, the first chip 100 isdisposed up side down. The second chip 200 is stacked on the backsurface 101 of the overturned first chip 100 and electrically connectedto the at least one fourth pad 171 via bumps 280. The stacked first chipand the second chip are thus electrically connected and integrated intoone circuit. The fifth pad 181 in the vicinity of the front surface 102is connected to a bump 180 for further connected to other circuit chipsor electronic modules. To align the electrical connection between thefirst chip 100 and the second chip 200, the fourth pad 171 iselectrically connected to the third pad 161 at the other end of thethrough substrate via hole 113 by the third metal layer 170 that extendsin a three-dimensional manner over one of the at least one electronicdevice 121 in the electronic device layer 120.

The semiconductor integrated circuit shown in FIG. 3 is fabricated bythe process as follows:

First, at least one compound semiconductor epitaxial layers is grown onsubstrate 110. Using the at least one compound semiconductor epitaxiallayer, at least one compound semiconductor electronic device (shown asat least one of the at least one electronic device 121 in FIG. 3) isfabricated on substrate 110. At least one second metal layer 150 madeessentially of Au is deposited above the at least one compoundsemiconductor epitaxial layer to form an electrical connection to atleast one of the at least one compound semiconductor electronic device121, and also to form at least one third pad 161. In FIG. 2, at leastone second metal layer 150 is made of three metal layers stacked oneafter another isolated by dielectric passivation/protection layerspreferably made of SiN.

The process above made on the front surface is then followed by thebackside process. First, substrate 110 is thinned down to a designedthickness by grinding, and at least one through substrate via hole 113is formed. Third metal layer 170 is then deposited on the backside ofsubstrate 110 and forms at least one fourth pad 171. Third metal layer170 also extends from at least one fourth pad 171 into at least onethrough substrate via hole 113, then connects to at least one third pad161. Here, third metal layer 170 is formed in such a way that it extendsfrom at least one of the at least one fourth pad 171 three-dimensionallyover at least one of the at least one compound semiconductor device(shown by 121 in FIG. 3), then into at least one through substrate viahole 113 and connects to at least one third pad 161.

The process steps above describe the essential part of the fabricationof first chip 100. Second chip 200 is then stacked on back surface 101of first chip 100. The electronic circuit in second chip 200 iselectrically connected to at least one of the at least one fourth pad171. Thus, the electronic circuit in second chip 200 is connected to thesemiconductor integrated circuit in first chip 100. The connection ismade via bumps 280. Bumps 280 are formed beforehand either on chip 100or chip 200.

In the fabrication method described above, electronic device layer 120is formed as a front-end process made on substrate 110. The processcontaining Cu, on the other hand, is made on the backside of thesubstrate 110. In this way, the contamination of compound semiconductordevice by Cu is prevented. The use of Cu for third metal layer 170reduces the signal loss due to the electrical connection between themain compound semiconductor integrated circuit and the second chip.

Each of the at least one fourth metal layer 170 in the previousembodiment may form a passive electronic element, such as an inductor.FIG. 4 is a schematic showing the cross-sectional view of anotherembodiment of the semiconductor integrated circuit, in which the fourthmetal layer 170 forms an inductor 172 on the backside of the substrate112. The inductor 172 is formed in a three-dimensional manner over oneof the electronic devices 121, and the inductor is electricallyconnected to the first chip. The inductor may also connect to the secondchip, or both the first chip and the second chip.

In the aforementioned embodiments, the first chip must be a compoundsemiconductor integrated circuit chip, and the second chip can be acompound semiconductor, a semiconductor, or other types of electronicintegrated circuit chip. The substrate of the first chip is made ofGaAs, Si, SiC, sapphire, or GaN. The substrate of the second chip isalso made of GaAs, Si, SiC, sapphire, or GaN, when the second chip is acompound semiconductor integrated circuit chip. The dielectric layer ofthe first chip is made of dielectric materials, preferably ofPolybenzoxazole (PBO). The preferable thickness of the dielectric layeris 10 μm or thicker for minimizing the influence of the first metallayer on the electrical characteristics of the electronic device in theelectronic device layer, over which the first metal layer extends in athree-dimensional manner to connect to the second pad at the other endof the dielectric layer via hole. The electronic device layer is acomposite layer including a compound semiconductor layer and apassivation layer. The passivation layer is made of dielectricmaterials, preferably of SiN, which can insulate and passivate theelectronic devices. The compound semiconductor electronic device can bea heterojunction bipolar transistor (HBT) or a high electron mobilitytransistor (HEMT). The compound semiconductor electronic device can be aGaN field effect transistor (FET) as well. The metal layers forelectrical connections in the first chip are divided into the metallayers in the electronic device layer and the metal layers not in theelectronic device layer. All of the at least one second metal layer 150directly in contact with the compound semiconductor electronic deviceare made essentially of Au and contain no or at least negligible amountof Cu to prevent the contamination of the compound semiconductor withCu, or all of the at least one second metal layer in the electronicdevice layer may be made essentially of Au with no or negligible amountof Cu. In the latter way, the formation of the electronic device layercan be performed as a front-end process without a metal layer madeessentially of Cu, thereby preventing the cross contamination of thefront-end process by Cu. The degradation of circuit performance andreliability due to the contamination by Cu is thus prevented. The metallayers which are not in the electronic device layer (the first metallayer 140 and the third metal layer 170) are not directly connected tothe compound semiconductor electronic devices but via the metal layersin the electronic device layer, and therefore they can be made of Cu toreduce the manufacturing cost. The formation of the metal layer made ofCu can be performed as the back-end process, thereby preventing thecontamination of the front-end process by Cu atoms. The thickness of theCu layer in the first metal layer is preferably 3 μm or thicker.

Further embodiments provided by the present invention are described asfollows:

Embodiment 1

FIG. 5 is a schematic showing the cross-sectional view of anotherembodiment of the semiconductor integrated circuit according to thepresent invention, in which the first chip 100 contains an HEMT MIMIC103, and the second chip 200 contains an HBT power amplifier (PA) MMIC203. The HEMT MMIC 103 has a substrate 110 made of GaAs. On thesubstrate 110 of the HEMT MMIC is an electronic device layer 120consisting of bias control, switch, and logic circuits constructed bypseudomorphic HEMTs (pHEMTs) 121. The HEMT MIMIC serves as a circuit tocontrol the bias condition of the HBT PA and/or to control the RF signalpath in the HBT PA. The electronic device layer 120 may contains one ormore SiN layers for the insulation and passivation of the devices. Onthe HEMT MIMIC, a dielectric layer 130 made of PBO is deposited on thesurface as an insulating layer. The dielectric layer is spin coated tothe thickness of about 10 μm. To provide electrical connection to theunderlying MMIC, plural dielectric layer via holes 133 are formed in thedielectric layer 130 penetrating from a first surface of the dielectriclayer 131 to a second surface of the dielectric layer 132 by aphotolithography technique using the photosensitivity of PBO. On thedielectric layer 130, the first metal layer 140 made essentially of Cuwith a thickness of around 5 μm are electroplated using sputtered TiW/Cuas a seed metal. The first metal layer 140 forms plural first pads 141for the electrical connection with the HBT PA MIMIC. The first metallayer 140 extends from the first pad 141 to a dielectric layer via hole133 over the active region of the HEMT MIMIC consisting of pHEMTs 121,capacitors 122, and resistors 123 in a three-dimensional manner to makeit possible to form the electrical connection between two chips havingthe connection nodes apart from each other. The first metal layer 140further extends into the dielectric layer via hole and connects to asecond metal pad 151 formed at the end of the dielectric layer via holeopposite to the first pad 141. In this embodiment, all of the secondmetal layers are made essentially of Au. Therefore, the second metal pad151 is also made essentially of Au. Each of the second metal pads 151 isfurther electrically connected through the second metal layers 150 to apHEMT 121, a capacitor 122, or a resistor 123 in the HEMT MIMIC. Thedirect contact of Cu with devices, particularly with the compoundsemiconductor devices, in the HEMT MMIC is avoided to prevent thedegradation of the device by Cu atoms. Furthermore, since all of thesecond metal layers are made essentially of Au, the front-end process,which is essentially the formation of the electronic device layer, canbe performed without a Cu process. The Cu process is separately done inthe back-end process. The Cu cross contamination of devices in theelectronic device layer is thus prevented, and the high stability andreliability in the circuit performance can be obtained. The second chip200 is stacked on the front surface 102 of the first chip 100. For theconnection between the two chips, a first bump 180 is formed on each ofthe first pad 141 of the HEMT MIMIC 103. The first bump 180 may be a Cupillar with a SnAg solder at the top of it. The second chip 200 has asubstrate 210 made of GaAs. Each of the first bump 180 is then connectedto a contact pad 271 formed by a back side metal layer 270 on thebackside of the substrate 210 of the second chip 200. Each of thecontact pad 271 extends into a through substrate via hole 233 formed inthe GaAs substrate 210 of the second chip, and then connects to a HBT221, a capacitor 222, or a resistor 223 formed in the HBT PA MMIC. Thestacked chips are turned over and the second chip 200 is flip-chipassembled with bumps 280, and connected to module pads 91 formed on amodule substrate 90.

Embodiment 2

FIG. 6 is a schematic showing the cross-sectional view of anotherembodiment of the semiconductor integrated circuit according to thepresent invention, in which the first chip 100 contains a HEMT MMIC 103and the second chip 200 contains an HEMT PA MMIC 203. The HEMT MIMIC 103consists of bias control, switch, and logic circuits, and serves as acircuit to control the bias condition for the HEMT PA MIMIC 203 and/orto control the RF signal path in the HEMT PA MIMIC 203. Otherdescriptions about the design of this embodiment are the same as that ofthe embodiment 1, except that the HBT PA MIMIC of the second chip 200 isreplaced by the HEMT PA MMIC.

Embodiment 3

FIG. 7 is a schematic showing the cross-sectional view of anotherembodiment of the semiconductor integrated circuit according to thepresent invention, in which the first chip 100 contains an HEMT MMIC 103and the second chip 200 contains an HBT PA MIMIC 203. The second chip200 is stacked on the front surface 102 of the first chip 100 and thestacked chips are turned over and the second chip 200 is assembled on amodule substrate 90 by wire bonding via bonding wires 204. Otherdescriptions about the design of this embodiment are the same as that ofthe embodiment 1

Embodiment 4

FIG. 8 is a schematic showing the cross-sectional view of anotherembodiment of the semiconductor integrated circuit according to thepresent invention, in which the first chip 100 contains a HEMT MMIC 103and the second chip 200 contains another HEMT PA MIMIC 203. The secondchip 200 is assembled on a module substrate 90 by wire bonding viabonding wires 204. Other descriptions about the design of thisembodiment are same to that of the embodiment 3, except that the HBT PAMMIC of the second chip 200 is replaced by the HEMT PA MMIC.

Embodiment 5

FIG. 9 is a schematic showing the cross-sectional view of anotherembodiment of the semiconductor integrated circuit according to thepresent invention, in which the first chip 100 contains an HEMT MMIC 103and the second chip 200 contains an HBT PA MMIC 203. The HEMT MIMIC 103has a substrate 110 made of GaAs and consists of switches 121,capacitors 122, and inductors 124. It serves as an impedance tuner thatachieves the impedance matching at the output of the HBT in the HBT PAMIMIC 203 operating at different bias conditions for the differentoutput powers and frequencies to maintain an optimal performance. Sincethe output impedances are functions of the bias condition and theoperating frequency, an impedance tuner is introduced to maintain a goodimpedance matching in accordance with the change in the operatingcondition. A dielectric layer 130 made of PBO is formed on the HEMT MMIC103. The spiral inductor 124 is formed on the dielectric layer 130 usinga first metal layer 140 made of Cu. The inductor 124 serves as a part ofthe impedance tuner circuit. In this embodiment, a direct electricalconnection between an I/O pad 91 on a module substrate 90 and aconnection node (one of the second pads 151) in the HEMT MIMIC 103 ismade using the first metal layer 140 that extends over the electronicdevices in the HEMT MMIC 103 in the three-dimensional manner andconnects the two nodes apart from each other. Other descriptions of thisembodiment are same to that of the embodiment 1.

Embodiment 6

FIG. 10 is a schematic showing the cross-sectional view of anotherembodiment of the semiconductor integrated circuit according to thepresent invention, in which the first chip 100 contains an HEMT MMIC 103and the second chip 200 contains an HBT PA MMIC 203. The descriptionsfor the HEMT MMIC 103 are same to that in the embodiment 5. The HBT PAMMIC 203 is similar to the HBT PA MIMIC 203 in the embodiment 3.However, a PBO layer 230 is formed on the HBT PA MIMIC 203, and a metallayer 240 made essentially of Cu is formed on the PBO layer 230. Themetal layer 240 is regarded as the first metal layer. Other descriptionregarding the type of metal, Au or Cu, for the first chip 100 alsoapplies to the second chip 200. Since the Cu metal layer is formed onthe front surface of both the first chip 100 and the second chip 200,there is more freedom in the layout design for connecting nodes in thecircuits in the two chips at different horizontal positions. The secondchip 200 is assembled on a module substrate 90 by wire bonding viabonding wires 204.

Embodiment 7

FIG. 11 is a schematic showing the cross-sectional view of anotherembodiment of the semiconductor integrated circuit according to thepresent invention, in which the first chip 100 contains an HBT PA MMIC103 and the second chip 200 is an electronic chip other than a compoundsemiconductor chip. The second chip 200 in this embodiment is a Si CMOSIC consisting of bias control, switch and logic circuits and serves as acontrol circuit for controlling the bias condition of the HBT PA MMIC103. A dielectric layer 130 made of PBO, the first metal layer 140 madeof Cu, and plural bumps 180 made of Cu/solder are formed on the HBT PAMMIC 103 sequentially. The first metal layer 140, which connect thefirst pad 141 and the second pad 151 at the other end of a dielectriclayer via hole 133 or to another first pad 141 to which the bonding wireis connected, is formed over the active region of a device in the HBTMIMIC 103 in the three-dimensional manner and connect the nodes in thetwo chips at positions away from each other. The electrical connectionsto the HBT PA MMIC are made through plural second pads 151 made of atleast one second metal layer. In this embodiment, all of the at leastone second metal layer, which provides connections to the HBTs 121 andother electronic devices 122 and 123, or forms the second pads 151 andthe third pads 161, are made essentially of Au, so that the Cu metallayer can be kept away from the devices in the HBT PA MMIC. Thedegradation of devices in the HBT MMIC due to Cu atoms can thus beprevented. The connections between the HBT PA MMIC 103 and a modulesubstrate 90 are made by wire bonding via bonding wires 104 and/or by athrough substrate via hole 113 in the substrate 110 via a fourth metallayer 170.

Embodiment 8

FIG. 12 is a schematic showing the cross-sectional view of anotherembodiment of the semiconductor integrated circuit according to thepresent invention, in which the first chip 100 contains an HBT PA MIMIC103 and the second chip 200 is a Si CMOS IC chip for the bias control ofthe HBT PA MMIC 103. The first chip 100 is turned over and the secondchip 200 is stacked on the back surface 101 of the first chip 100. Theelectrical connections between the two chips are made at the fourth pads171 each formed by a third metal layer 170 on the back side of thesubstrate 110. Each of the fourth pads 171 is electrically connectedthrough a through substrate via-hole 113 to the third pads 161, then tothe electronic devices and the second pads 151 in the electronic devicelayer 120, all formed by the at least one second metal layer 150. Inthis embodiment, all of the at least one second metal layer 150 are madeessentially of Au same as the embodiment 7, thereby preventing thecontamination of the compound semiconductor devices with Cu. The firstmetal layer 140 made essentially of Cu is formed on a dielectric layer130 made of PBO. The first metal layer 140 forms a first pad 141 whichcan be used for electrical connection to a module substrate 90. Thedielectric layer 130 has plural dielectric layer via hole 133penetrating through the dielectric layer 130. The first metal layer 140extends from the dielectric layer via hole 133 to a first pad 141connected to one of the I/O pads 91 on the module substrate 90 over theactive region of a device in the HBT MIMIC in a three-dimensional mannerto make an electrical connection between one of the fourth pads 171 onthe back side of the substrate 110 and the I/O pad 91 on the modulesubstrate 90 at different horizontal position. The first chip 100 isflip-chip assembled on the module substrate 90 with bumps 180 formed onthe first pads 141 and on the emitter layers of the HBTs 121 throughdielectric layer via holes 133.

Embodiment 9

FIG. 13 is a schematic showing the cross-sectional view of anotherembodiment of the semiconductor integrated circuit according to thepresent invention, in which the first chip 100 contains an HBT PA MMIC103 and the second chip 200 contains integrated passive devices (IPD) ora filter. The integrated passive devices can be formed on a substratemade of glass, silicon, or compound semiconductor such as GaAs. The IPDserves as a filter, an impedance matching circuit, etc. The second chip200 may also contain an acoustic filter such as a surface or a bulkacoustic wave filter, a film bulk acoustic wave filter, etc., and can befabricated on a substrate such as Si. The second chip 200 is stacked onthe front surface 102 of the first chip 100. The descriptions for thefabrication process of the first chip are same to that in embodiment 7.

Embodiment 10

FIG. 14 is a schematic showing the cross-sectional view of anotherembodiment of the semiconductor integrated circuit according to thepresent invention. The design of this embodiment is similar to that ofthe embodiment 9, except that the HBT PA MIMIC in the first chip 100 isreplaced by a HEMT PA MIMIC 103.

Embodiment 11

FIG. 15 is a schematic showing the cross-sectional view of anotherembodiment of the semiconductor integrated circuit according to thepresent invention. The design of this embodiment is similar to that ofthe embodiment 9, except that the first chip 100 is flip-chip assembledon the module substrate 90 as described in the embodiment 8.

Embodiment 12

FIG. 16 is a schematic showing the cross-sectional view of anotherembodiment of the semiconductor integrated circuit according to thepresent invention. The design of this embodiment is similar to that ofthe embodiment 11, except that the HBT PA MMIC in the first chip 100 isreplaced by a HEMT PA MMIC 103.

Embodiment 13

FIG. 17 is a schematic showing the cross-sectional view of anotherembodiment of the semiconductor integrated circuit according to thepresent invention, which includes multiple stacked chips. In thisembodiment, the semiconductor integrated circuit comprises a first chip100 containing an HBT PA MMIC 103, a second chip 200 containing animpedance matching circuit (integrated passive devices) and a biascontrol circuit, a third chip 300 containing an antenna switch circuit,and a fourth chip 400 containing a filter. The second chip 200 isstacked on the back surface 101 of the first chip 100, the third chip300 is stacked on the second chip 200, and the fourth chip 400 isstacked on the third chip 300. The descriptions for the fabricationprocess of the HBT PA MMIC 103 are the same as that in the embodiment 8.The connection to a module substrate 90 is made both by bumps 180 formedon the front surface 102 of the first chip 100 and by wire bonding viabonding wires 404 made on the filter chip 400.

Embodiment 14

FIG. 18 is a schematic showing the cross-sectional view of anotherembodiment of the semiconductor integrated circuit according to thepresent invention, in which the first chip 100 contains an HBT PA MMIC103 and the second chip 200 is an electronic chip. The first chip 100 isturned over and flip-chip assembled on a module substrate 90. The secondchip 200 is stacked on the back surface 102 of the overturned first chip100. The second chip 200 consists of bias control, switch, and logiccircuits and serves as a control circuit for controlling the biascondition of the HBT PA MMIC 103, and/or a switch circuit that switchesthe RF signal paths in the HBT PA MMIC in the first chip 100. The secondchip 200 is either a compound semiconductor MIMIC such as an HEMT MMICor a Si CMOS IC. In the first chip 100, the third metal layer 170 formsat least one fourth pad 171 on the back surface 102 of the first chipand extends into the through substrate via hole 113. One of the secondmetal layers 150 forms a third pad 161 at the end of the throughsubstrate via hole 113 opposite to the fourth pad 171, at which thethird pad 161 is electrically connected to the third metal layer 170that extends into the through substrate via hole 113. The third pad 161is electrically connected to HBT 121 by the second metal layer 150. Thethird pad is also electrically connected to the fifth pad 191 formed atthe surface of the electronic device layer opposite to the substrate.The fifth pad 191 is further connected to the I/O pad 91 on the modulesubstrate 90. The fourth pad 171 is electrically connected to the secondchip 200 through bumps 280. The third metal layer 170 is formed over aresistor 123, capacitor 122, and HBT 121 in the first chip in athree-dimensional manner. In this way, the connection between the twochips having connection nodes at horizontal position apart from eachother can be made. The third metal layer 170 is preferably made ofplating Cu with Pd as a seed metal.

Embodiment 15

FIG. 19 is a schematic showing the cross-sectional view of anotherembodiment of the semiconductor integrated circuit according to thepresent invention, in which the first chip 100 contains an HBT PA MMIC103 and the second chip 200 contains an impedance matching circuitconsisting of inductors and/or capacitors formed on a substrate made ofSi, GaAs, or glass for matching the output impedance of the HBT in thefirst chip 100. The second chip 200 is stacked on back surface 101 ofthe overturned first chip 100. The second chip 200 may also contain animpedance tuner used to obtain the output impedance matching to the HBTin the first chip 100 at various different operation conditions. Thesecond chip 200 may also contain a filter circuit that filters outunwanted signals generated by the HBT in the first chip 100 atfrequencies different from the fundamental frequency, consisting ofeither integrated passive devices formed on a Si, a GaAs, or a glasssubstrate, or an acoustic filter such as surface, bulk and film bulkacoustic filters. The description for the fabrication process of thefirst chip 100 is the same as Embodiment 14.

Embodiment 16

FIG. 20 is a schematic showing the cross-sectional view of anotherembodiment of the semiconductor integrated circuit according to thepresent invention. The design of this embodiment is similar to that ofthe embodiment 15, except that the HBT PA MMIC in the first chip 100 isreplaced by a HEMT PA MMIC 103.

Embodiment 17

FIG. 21 is a schematic showing the cross-sectional view of anotherembodiment of the semiconductor integrated circuit according to thepresent invention. The design of this embodiment is mostly similar tothat of the embodiment 15. In this embodiment, the fourth metal layers170 forms a spiral inductor 172 on the back surface 101 of the firstchip 100. The inductor 172 is electrically connected to the MIMIC in thefirst chip 100 through a through substrate via hole 113. The inductor172, the MMIC in the first chip, and the second chip form an impedancematching and tuning circuit. The metal layers 170 are made preferably ofCu or multiple metal layers containing Cu layer for low signal lossowing to its high conductivity.

Embodiment 18

FIG. 22 is a schematic showing the cross-sectional view of anotherembodiment of the semiconductor integrated circuit according to thepresent invention. The design of this embodiment is similar to that ofthe embodiment 17, except that the HBT PA MMIC in the first chip 100 isreplaced by a HEMT PA MMIC 103.

Embodiment 19

FIG. 23 is a schematic showing the cross-sectional view of anotherembodiment of the semiconductor integrated circuit according to thepresent invention, which includes multiple stacked chips. The design ofthis embodiment is similar to that of the embodiment 13, except that thefirst chip 100 is designed similarly to the first chip 100 in theembodiment 17.

To sum up, the present invention can indeed get its anticipated objectto provide a semiconductor integrated circuit, which comprises stackedelectronic chips, in which at least one of the chips is a compoundsemiconductor electronic integrated circuit chip. The present inventionhas the following advantages:

1. By using the stacked chips scheme to compose a module, the elementsin the module can be formed on separated chips. Since each of the chipscan have its optimal layout design and can be fabricated with processesonly required for the each chip, the overall manufacturing cost can bereduced compared with the case in which the circuit elements areintegrated in one chip. The areal size of the whole module can also bemade smaller than the case in which the chips are placed laterally onthe module substrate.

2. The interconnections between chips or between two circuit elementscan be made by using the metal layers formed on the front surface or theback surface of the chips. The front surface/back surface metal layerscan be formed over the device active region which makes it possible toconnect nodes in two chips at positions apart from each otherhorizontally. Therefore, there is more freedom in the layout design ofthe connection nodes. The interconnections can be made short to reducethe signal loss and interference compared to the case in which chips areplaced laterally on a module substrate.

3. While Cu is used for the interconnections between chips, Au is usedfor the metal layers in contact with the compound semiconductor devices.In this way, the degradation of the electrical performance of thecompound semiconductor by Cu atom in-diffusion is prevented.Furthermore, by completely avoiding the use of Cu layer in the formationof the electronic device layer, which is the essential part of thefront-end process, the process steps involving the formation of Cu layeris brought into the back-end process. Thus, the cross-contamination ofthe front-end process by Cu atoms is completely prevented. A highlong-term reliability is maintained even though the Cu metallizationprocess is used in the compound semiconductor MIMIC process.

4. The metal layer on the back surface of a chip can be used to form aninductor or other passive electronic devices. The inductor on the backsurface of the chip further save the space occupied by the wholecircuit, and therefore the chip size can be reduced. The high qualityfactor for the inductor on the back side of the chip can be obtainedwhen the back side metal layer contains Cu.

The use of the compound semiconductor integrated circuit chip with thefront surface metal layer over the device active region can also beextended to cases without a stacked chip. The compound semiconductorintegrate circuit chip can be connected to any electronic circuitsthrough the front surface metal layer, such as the case when the chip ismounted on a module substrate with the electrical connection made bybump bonding or wire bonding between a pad formed on the modulesubstrate and a pad formed with the front surface metal layer. Thus,more freedom in the layout design of the pad location is obtained.

The description referred to the drawings stated above is only for thepreferred embodiments of the present invention. Many equivalent localvariations and modifications can still be made by those skilled at thefield related with the present invention and do not depart from thespirits of the present invention, so they should be regarded to fallinto the scope defined by the appended claims.

What is claimed is:
 1. A method for fabricating a compound semiconductorintegrated chip, sequentially comprising steps of: growing at least onecompound semiconductor epitaxial layer on a substrate of a chip;fabricating at least one compound semiconductor electronic device on thesubstrate using the at least one compound semiconductor epitaxial layer;depositing at least one second metal layer made essentially of Au abovethe at least one compound semiconductor epitaxial layer to form anelectrical connection to at least one of the at least one compoundsemiconductor electronic device, and also to form at least one secondpad; depositing a SiN layer above the at least one second metal layerfor passivation or protection of the at least one compound semiconductorelectronic device; depositing a dielectric layer above the SiN layer;forming at least one dielectric layer via hole penetrating through thedielectric layer for the electrical contact to the at least one secondpad; and depositing a first metal layer made essentially of Cu on thedielectric layer forming at least one first pad on the dielectric layer,the first metal layer extending from each of the at least one first padinto the at least one dielectric layer via hole and connecting to the atleast one second pad, where the first metal layer extends from at leastone of the at least one first pad three-dimensionally over at least oneof the at least one compound semiconductor device, then into the atleast one dielectric layer via hole and connects to the at least onesecond pad.
 2. The method of claim 1, wherein the substrate of the chipis made of GaAs, Si, SiC, or GaN.
 3. The method of claim 1, wherein thedielectric layer is made of Polybenzoxazole (PBO).
 4. The method ofclaim 1, wherein the thickness of the dielectric layer is 10 μm orthicker.
 5. The method of claim 1, wherein the first pad is forconnecting another chip to the chip.